


The Only Good Mistake

by Ollieisverybored



Category: Undertale (Video Game)
Genre: Chara Protection Squad, Dadster, Discussion of Abortion, Gen, Minor Asgore Dreemurr/Toriel, Minor Sans/Toriel, Nonbinary Frisk, Post-Soulless Pacifist Route, night terror sans, skelepreg
Language: English
Status: In-Progress
Published: 2016-01-25
Updated: 2016-03-15
Packaged: 2018-05-16 05:12:14
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 4,827
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5815522
Author URL: https://archiveofourown.org/users/Ollieisverybored/pseuds/Ollieisverybored
Summary: <blockquote class="userstuff">
              <p>Frisk has promised this would be the last reset. The one that would save W.D Gaster and have them all stay on the surface, so Sans has been relaxing on his magic use and living life with a little more hope. But things can happen when you let your magic build up, and Sans isn't sure if he's confident with the choice he made.</p>
            </blockquote>





	1. Small Shock

**Author's Note:**

> A/N this goes off my headcanon that if a monster has too much excess magic, a second soul is created with it. It's mainly being used in another skelepreg Sans fic, but I wanted to use the idea for this fic too, cause I didn't want to create a random skeleton/monster oc for one use in a fic, or have Sans being shipped with anyone in order to focus on the development of his character. It also goes off my headcanon that Sans and Toriel did know each other very well, but knew nothing much of their physical descriptions other than Skeleton and Goat.

There were many mistakes Sans made in his life, so far they were bad, but Sans knew that keeping this kid was the only good mistake he'd made so far. No matter how hard it would be to hide, or to tell people, he was gonna have this kid and raise them the best he could. When he first realised his low energy was due to a new soul forming, he cursed himself for not using his magic on a regular basis. His unnaturally high amount of magic was capable of doing many things if left alone, from random Gaster Blaster outbursts, to forming long ghost hair that could envy Rapunzel, but the one side effect he hoped he'd never encounter would be a child. The amount of magic left over had to be great in order for a new soul to be made. Frisk had promised this would be the last reset, as they were going to save Gaster form the void, and they'd be sending them back a month early in order to plan his rescue, so Sans wasn't too bothered about using his magic regularly. This proved to be a complication.

He clocked that something was off when his ecto-stomach started to cloud and he had to stare in order to make out his spine. It had taken about a week to happen, and if it wasn't for the faint green glow in the middle of his stomach, he could have dismissed it as illness, but he knew how monster skeletons worked, and he was displaying the early signs of pregnancy. He didn't know what to do, and he didn't know anyone he could turn to about this, all he knew was that he was scared and worried for the child. He felt terrified having to carry this child, and was afraid he wouldn't be a good parent as his bad mental health made it hard to take care of himself; he believed that if he couldn't take care of himself well, it would be cruel to try and bring his child into the world. His worries for the child's quality of life lead him to disguising himself in a ridiculous orange hoodie and green cargo pants, in order to safely travel to a potions chemist in waterfall, one who could provide him with a soul-erasing potion. 

\----

“Hello sir, what can I do for you today?” A axolotl monster asked, peering up behind her glasses  
“my girlfriend sent me here to buy a luos potion.” Sans lied, taking deep breaths to his nervousness in his voice, “she would have come herself but she has horrible morning sickness, so i offered to go for her.”  
“Okay then sir,” the chemist replied, “you'll just have to wait for an hour for it to be prepared. Not many monsters use soul-erasing potions anymore, so we now make them per order. Is there anything else you need? How far along is she?”  
“a month, give or take a few days.” Sans said, pulling his hood further over his head,  
“Well depending on what type of monster she is, you’ll both have plenty of time to debate on whether you want to keep the baby.” The monsters gills twitched as she prepared an echo flower for the luos potion,  
“she's a skeleton monster like me, so she'll need to have taken the potion by the 4th month, right? skeletons carry for 6 months.”  
“Yes she will, so I recommend you get a stomach calming potion as well to help her through the morning sickness.”  
“sure, sure.” He replied, feeling sickness rise in his stomach, “do you have a toilet i can use? i’ve got a bit of soul-sympathy sickness.” It was common for a monster to feel some of their partners symptoms to a small degree, provided the couple were close, so this made a good cover for the oncoming sickness. The lady pointed to a door on Sans’ left, and he rushed in, barely holding himself together before vomiting. He didn't understand why skeleton monsters got morning sickness, nor why it was called morning sickness despite going on for most of the day, but he felt as if focusing on being sick was a more pressing matter. When he finished and cleaned up, the monster had rang his total price up, “That'll be 500g please. Your positions should be ready in an hour.” Sans handed over the 500g, silently wishing Papyrus wouldn't notice the money missing, and decided to take a shortcut to the Snowed Inn Shop, where he used to work part-time. 

\----

As the doorbell rang to announce his entrance, the shopkeeper turned to wave at Sans and called out, “Have you come to beg me for another cinnamon bunny? I can see they're giving you extra winter warmth, or is that Grillby's doing?”  
“well hello to you too, Lopsy. last time i checked, i payed for all my cinnabunnies!”  
“With Sans coupons, ‘redeem for one free hot dog…?’ Those aren't legitimate forms of payment. It's a good job I love ya too much.” Lopsy opened the hatch to her side of the shop and let Sans in, pulling a seat out as he helped himself to a pastry. Business was quiet, so Lopsy and Sans made idle chat in between customers, chatting about Papyrus, the dog they had somehow half adopted, town gossip and made jokes. Sans got his love of jokes from Lopsy, and when he first came to Snowdin with Papyrus, she guarded the two children with her life and proudly earned the title of ‘Auntie Lopsy’. Sans knew he could trust her with gossip worthy news, and pondered outright asking her for advice on whether he should keep his unborn child. As she served customers, he mulled over the thought, concluding that keeping it hushed was a safer plan in case he decided to abort. Lopsy could always sense if something was up with the skeleton, and was willing to comfort him on any troubles, and immediately sensed something was wrong with Sans, “D’you feel like telling me what's up, or would you rather keep it to yourself?” She asked, hoping he would open up, “i wanna tell you, but it's something the gossipers would rip to shreds of they found out. not that you'd tell or anything, but it's like they have the biggest ears and eyes ever. i bet rumours are already going around!” He replied, panic rising in his mind. Lopsy wanted Sans to open up, but understood his paranoia, “Be vague then. You are practically a master of being vague.”  
“okay… well let's use my pet rock for demonstrations sake. last month i got a pet rock, the best pet rock ever, but with my depression i can barely take good care of myself, let alone a rock. yet i know i'll always feel bad in the back of my head of i got rid of him cause i couldn't take care of him, and i know Paps does a lot for the rock, but i feel bad having to push the responsibility onto him. i know if i were to try harder, i could make it work, but it could take a horrible toll on my mental health, and i don't know what I'd do about that. what's the best advice you could give me?”  
Now Lopsy wasn’t stupid, she knew this had something to do with a child, but she thought his blue glow was a sympathy glow, assuming he'd created a soul with a monster who was willing to carry to term for Sans to father. She kept her mouth zipped half way when replying, “Well you've obviously put some good thought into this, and you've had your pet rock for a month now, so you I think you really want to make this work and try hard. I suggest that you leave it a few weeks and try to improve your mental state. You could start by deep cleaning your room. I found that if I'm unsure of something, giving a room in my house a deep clean gives me time to process the situation I'm tackling and I can answer it afterwards.”  
“t’anks a bunch Lopsy...you don't happen to-”  
“If you don't go now, you'll throw up all over my counter. Sympathy sickness is bad, but it won't work as an apology for ruining my cinnamon bunnies.” she quipped, watching Sans run to the bathroom.

As Sans made his way up to Lopsy’s bathroom, he felt a small shudder of fear run down his spine, ‘She knows about the baby, but thank god she thinks I knocked someone up.’ He thought, pushing the bathroom door open before throwing up the cinnamon bunny. 

\----

He’d just picked his stuff up from the potions chemist, when he quite literally bumped into Undyne, who was on her way to buy some healing potions. He'd hid the potions in a paper bag, so he wasn't bothered about her accidentally seeing them, and his disguise was surprisingly better than he thought, as she just mumbled ‘lousy Capital skeleton’ after bumping into him. Once she was in the chemist, he put a hand over his tummy, rubbing over the tiny bump that had formed. He was glad he wore baggy clothes, as he could easily hid the suspicious bump. For a man who wanted to be rid of the soul, he sure felt a pinch of worry when Undyne bumped into him. He took a shortcut back to his home, and made his way up to his room, opting to take Lopsy’s advice and got to work on deep cleaning his room. He started by changing his sheets, seeing as though he hand my done that for a few months. When going to put them in the washing machine, he startled Papyrus, "SOMETHING IS UP, YOU'RE CHANGING YOUR SHEETS AND YOU NEVER DO THAT." He pointed out, gesturing to the stained sheets, "don't worry bro, i guess i should come clean." he replied  
"SANS!"  
"come on that was a wonderful pun. i kinda have a personal dilemma i need to sort out, so Lopsy recommend cleaning my room to clean my head. i don't know why i need to clean it, i've got nothing but air in here!" He joked, pointing to his skull. Papyrus stared suspiciously, but soon sighed, "WELL I HOPE YOU FIND YOUR ANSWER SANS."  
"thanks Pap." And with that, Sans was walking up to his room again. He checked his calendar, noticing that tomorrow would be the day the human fell, and he hoped to god they knew what they were doing. He had switched to autopilot when cleaning, and didn't realise he'd been cleaning for about 3 hours when Papyrus opened his door to announce that he'd been calling Sans for dinner for the past 5 minutes, and that his 'artisanal spaghetti' was being ruined by the cold, so Sans took a break to eat the food, grateful for the care put into making it, but not for the putrid taste that made him dash to the kitchen sink, rudely vomiting it all up. Papyrus came over to him, worried for his brothers health, and began running circles on his spine and ribs, "I KNEW SOMETHING WAS UP! YOU'RE JUST SICK, PROBABLY FROM EATING THAT GREASE YOU CALL FOOD. THAT’S IT, NO MORE GRILLBY’S FOR YOU!" He proclaimed, earning an angry sigh from Sans, "relax Paps, it's probably a virus going round. i was hanging with Grillby's kid and she had it, so i probably caught it off her. please don't take my junk food away from me."  
"WELL IF YOU REALLY ARE SURE. YOU BETTER GET OFF TO BED IF YOU WANT TO RECOVER." Papyrus helped to balance Sans as he guided him up to his room, "YOU EVEN GOT RID OF THE TRASH-NADO! EITHER YOU REALLY DO HAVE A VIRUS, OR A SHAPESHIFTER DID A REALLY BAD JOB OF REPLACING YOU." He said as he helped Sans get into bed. He wished him a good night's sleep, and closed the door behind him, leaving Sans on his own with his thoughts 'I may as well take that calming potion if I'm gonna want to make it through tomorrow.' He thought as he drifted off to sleep.

\----

He was outside the ruins, waiting patiently for a sign of Frisk, when he heard an all too familiar voice call out, "Knock knock!" It said, stud inking laughter, "okay Tori. who's there?" He replied, lowering himself gently to the round, "Theodore"  
"theodore who?"  
"Theodore is jammed and won't open!" She exclaimed, comically shaking the door for effect. They both took a few deep breaths, trying to regain their posture after the joke, which Sans had never heard her say 'Must've been one the kid told her.' He was busy thinking of another joke when Toriel began speaking, "Another human fell down today. I think they want to say with me for a while."  
This was new.  
"They told me that they do want to go home, but that it can wait a while as they're in no rush. I don't want to let them go though. It feels as if I've already known them for so long, and that letting them go could hurt them. Do you ever get that feeling Sans?" He already knew the answer,  
"yeah I do, but you're probably getting it cause you've dealt with this six times before." So was this part of Frisk's plan, wait with Toriel for a while. Were they going to convince her to come with them? Or were they buying more time to formulate their plan? Either way he wanted the kid out of there soon. He made idle chat and joked with her for about an hour, until she went to check on the small one, and they finally decided to exchange numbers should the child ever decide to exit the ruins, so he could keep an eye socket on them. This was by far the smartest reset the kid had done. He decided to walk back to his house in order to give him more time to think the ordeal with his child over, and was so focused that he ended up ignoring Lopsy when she called out to him, more bothered about getting home. He got to his front door and picked off a note taped to the door, 'You weren't in when Undyne called me for an early training session, as she's got to go to a talk at a school when our lesson is on. I'll be back in a few hours - The Great Papyrus' Sans sighed in relief, he had time to do this in his own. He went up to his room, and grabbed the paper bag from his desk drawer, taking out the Luos potions. He stared at the glittering liquid, wisps of purple and gold flowing through the dark blue, 'it's now or never' he thought, uncapping the bottle and lifting it up to his mouth. He had the bottle at his lips, but he couldn't seem to tip it up to drink it, and the longer he held it, the more his hand lowered and shook. He tried to drink it a few more times, but with each try, he began to cry harder and harder, "i can't do it." He choked, hand shaking as he put the cap back on the potion, "i don't want to do it. i- i don't wanna get rid of you." He was stuttering now, tears falling down his face, "i'm n-not gonna give up on-on you kid. i mi-might not t-take much care of myself, bu-bu-but i s-wear to god i will prote-tect you within an i-inch of m-my life." He took one last look at the potion and teleported to the chemist, collecting a refund on the potion and teleported back home, running to the bathroom in order to throw up. 

\----

By now he'd taken the calming potion, and had laid down on his bed, hoping to get a few hours sleep before Papyrus came back home, when he felt the first signs of life in the soul. He felt it send waves, trying to send a signal to Sans, and his face heated up, a soft, comforting smile washing over his face. The soul seemed hungry, so he sent some of his magic to it. A monster had to set up a magical connection to its child when their soul began to send waves, and for skeletons that came around the 1 month mark. His soul glowed a cyan blue and small tendrils of magic trickled down through his ribs and tummy to the soul, it's faint green glow beginning to clear and solidify, a wispy heart shape slowly forming. He looked at the soul, tears forming in his eye sockets, and for the first time felt a true and powerful need to protect the soul. The soul responded to Sans’ tears ‘Happy’ ‘Safe’ it said, as Sans placed a hand to his tummy, slowly rubbing the small bump, “i could be risking a lot to bring you into the world. it's a good job i love you.” He whispered, a small smile of genuine happiness showing on his face, cyan blue dusting his cheeks as he went to hug his tummy, “i don't know if i really am ready to have a kid, but i swear to god i will try for your sake.” The soul sent small waves of happiness to Sans’ own soul, and he knew right then that he'd never look back on this decision. There were many mistakes Sans made in his life, so far they were bad, but Sans knew that keeping this kid was the only good mistake he'd made so far.

**Notes for the Chapter:**

> EDIT 15/03/16
> 
> The souls glow has changed from purple to green to fit with the rest of the fic  
> the soul moving has all changed t the soul sending waves (thoughts)


	2. Reunited

**Summary for the Chapter:**

> What happens when a murderous flower tries to reform and change his ways for a time traveling child, a ghost sibling and their friends he promised to be nice for? CHAPTER TWO HAPPENS THATS WHAT

**Notes for the Chapter:**

> Sorry this took too long to update. I never felt happy with it and I'm still not happy with it, but I didn't want to leave it any longer. I'll try to make this update weekly from now on. I hope you enjoy this chapter and just to let you know, I have a new series of mini fics unrelated to this Fic coming out in the next week revolving around pre-core characters and science lab rules.

If it wasn’t for the loud ring of his phone, Sans would have stayed in bed for as long as possible, but a call from Toriel informing him of Frisk’s desire to go home had him out of bed and traveling to the edge of Snowdin forest. He took a shortcut, sitting at his sentry station for a while as he waited for Frisk to exit. An hour passed by with Sans’ mind drifting elsewhere, when a loud creaking sound rang through his skull; he quickly composed himself and got up, walking to meet the kid with a friendly handshake. He expected to see Flowey woven up their right arm, but the sight still startled him as he saw the former prince pulling faces as he talked with Frisk. 

During the last few resets, Frisk had been trying harder to befriend Flowey after seeing him break down during the last no-mercy reset. They had finally gotten Chara to understand that they were being manipulated by intrusive thoughts, that all the monsters had cared for and still cared for Chara; the death of both princes still affected monsters years later. 

Sans walked to the two as they chatted with what he could only assume to be Chara’s ghost. His outstretched hand was met with a hesitant leaf as Frisk guided Flowey to shake hands with the skeleton, “aw, is this yellow flower for me, Frisk? ya shouldn’t have.” he joked, a frown forming on Flowey’s face as he slowly realised the double meaning.   
“Ha ha very funny skeleton. Yellow flowers mean friendship and all that crap, but just so you know, I’m only trying for the sake of Chara and Frisk.”  
Well, at least he wasn’t hurting anyone.  
“Frisk told me I’ll have to solve some puzzles soon, but I’d rather not bother with something boring and stupid.”  
Sans’ face dropped slightly into a small scowl, shouting a reply at Flowey “my bro made those puzzles ya pansy!”  
“Do I have to solve them, Frisk?” asked Flowey, turning and pouting at them, to receive a nod in reply; Flowey knew that trying to argue would be pointless. 

The four of them went through the usual routine of Frisk hiding behind the lamp, Sans joking with his brother, and now had Flowey planted in the ground, acting as flower-like a possible. After Papyrus had left, human flower and ghost following behind, Sans walked to his sentry station and leaned over to grab a bottle of ketchup, hand absentmindedly resting on the small bump as he drank. He took a shortcut to his next needed location, understanding the danger this could put him in during the later months to come.

Frisk and Flowey entered to Sans and Papyrus chatting away, followed through with the expected dialogue, watching Papyrus’ face light up at the sight of his old friend Flowey, and left to continue with more puzzles. 

\----

Exiting Lopsy’s shop with some healing food and and a manly bandana, Frisk and Flowey finally had time to take in the sights of Snowdin. The town looked the same as ever to the human, but Flowey had never given himself a chance to take a proper look around the town in so many years of resetting, and it felt as if Snowdin was a new place to discover. “Guess they still have my sign up over there.” He remarked, pointing to the library sign a short distance away as Frisk laughed, “So I’m guessing you never learnt to spell library, or ‘Librarby’ as you call it.” they replied  
“I might act like an adult but I’m still only 15!”  
“You’re 15? I’d have never guessed Asri-you were that old!” Frisk catching themselves from separating Flowey and Asriel,  
“The goat was short for his age.”  
“That still doesn’t explain the misspelt sign.”  
“We have dyslexia.”  
“Ah, got it!”

As the two continued chatting, Sans had just sat down in Grillby’s. He waved to the bartender to grab his attention, “hey grillbz, can i get an order of fries?”  
‘Why no burger?’ the fire elemental signed  
“i don’t think i can stomach it dude.” he joked, a small crackle escaping from Grillby.  
In all truth, the small souling was giving Sans a hard time; he couldn’t seem to eat his usual meals without feeling nauseous. He regretfully had to cut down on his daily intake of ketchup, considering the small soul couldn’t handle the amount he ingested on a daily basis, only drinking the condiment when around others to snub the rumors that Sans was falling. He had just seen his plate of fries placed before him when a tall, lanky figure sat beside him.

Papyrus called Grillby over and ordered a vanilla milkshake, the smaller skeleton noticing his brother's legs dangle and swing slightly. Papyrus tuned to Sans and instantly spoke to defend his actions, “MILKSHAKES AREN’T GREASY! THEY’RE GOOD FOR THE BONES.” Sans laughed at his brother's sudden defensive outburst, aware of Papyrus’ frequent visits to the famed snowdin diner. Grillby could be a gossip if the information wasn’t serious.   
Sans was idly chewing as fiery and boney hands signed rapidly, the bartender engrossed in a conversation with the taller skeleton about his recent cooking lesson with Undyne, and how he still kept silent about the legitimacy of her cooking skills, ‘I HAVE THE MERCY TO SPARE HER FROM TEARS, GRILLBY!’ He signed, ‘BESIDES, WE HAVE FUN TOGETHER! IT MAKES ME FORGET THAT SHE WON’T LET ME JOIN THE ROYAL GUARD.’ 

Sans watched on, laughing with his brother and friend when he felt the soul send waves of happiness. He glanced about worryingly, and rested his free arm on the bar, as his hand came to lie at the top of his tummy. He listened on the conversation, butting in every so often, and didn’t realise when his hand lowered slowly rest more towards the middle of his abdomen.  
He had just finished his fries when he realised where his hand had been resting, and made to take it away, but it felt wrong to sever the physical contact. He told Grillby to put the fries on his tab and made his way outside, zipping his hoodie up to protect the soul from the bite of Snowdin’s air. He made his way over to his house, spotting Frisk and Flowey sat on the front step, “is your butt frozen yet?” He called out,   
“No! But Flowey said he feels like a snow-drop.” Frisk replied  
“I did not say that!” The flower screamed  
“Forget Asriel Dreemur,” Sans began, “Your Asriel Screamer!” There was a small fight, but Flowey let loose and joined in on the laughing, he might have lost emotion, but he still appreciated a good joke.

The three made their way to the back of the log house, and went into Sans’ lab, working on ways to communicate with Gaster for a few hours, and were invited to spend the night on the font brothers sofa, but declined as they had a room rented for the night at Snowed Inn.

\----

The next day, Sans watched the two battle and spare Papyrus, go on the most unsuccessful date with him, and wander off to waterfall. He knew he’d see them in a few hours during his shift at his hotlands sentry station and to speak at the MTT Resort, so he took the river person’s ferry service there in order to get in a few hours rest. The warmth of Hotlands comforted Sans, and as he discovered a while ago, settled the souling. He walked to his station and sat down, resting his head on his folded arms and slept until Undyne came to complain to him about his tendency to fall asleep during duty, letting the flower and child escape. He met with the two again and challenged them to a balancing competition, Frisk narrowly winning.

He ran over the new usual conversation topics at the restaurant, what had changed since last reset, and who they were trying to save this time, but his voice was no longer bitter with anger at the resets. They told Sans about the room in Waterfall’s caverns, the one Frisk originally found Gaster trapped in, and had recently come to the realisation that Gaster needed to be brought out of the room by someone connected to him, and his son Sans was an obvious choice. The three had theorised that if he chose to come out of his room, the memories every monster had of W.D Gaster would return, but it was up to Gaster to decide if he wanted to leave and start his life up again. So long as he could see his father again, Sans would be satisfied.

They all made their way to the grey door in waterfall, uncertainty sitting heavy in the air as Sans grabbed the doorknob. He slowly pushed the door open, and met with his father sat down. He’d seen and spoke with him in dreams, but knowing how real this was sent him over the edge, breaking out into sobs as he hugged him tightly. Sans knew he’d have be able to keep his emotions in check if he wasn’t pregnant, but he allowed himself to cry as Gaster hugged him tightly. 

They sat and talked with Flowey and Frisk for a while, but Gaster ultimately decided upon staying in the void. Coming back into the world after being erased would take an emotional toll on the ex Royal Scientist, and there would be so much explaining to do. He was devastated, but knowing he could see his father one last time put Sans at ease. The baby soul had been oddly steady during the visit, but once Sans had said goodbye to his father, Frisk and Flowey, they sent large waves of excitement to their father, “slow down there buddy.” He whispered whilst walking through Waterfall, “you’re gonna tire yourself out.”

As he approached the pathway between Snowdin and Waterfall, he saw Papyrus running up to him, realisation suddenly hitting him. He had yet to tell Papyrus that he was to be an uncle, and it wasn’t as if he was anxious about it, Papyrus knew all about the ways monsters had children, he wasn’t oblivious and innocent. He could never find the right time to pull his younger brother aside to tell him, but maybe now would be good. 

“hey paps.” He called out, waving to him as the taller skeleton slowed down upon approach, “HELLO SANS! I WOULD LIKE TO KNOW IF YOU ARE COMING TO JOIN ME AND UNDYNE FOR DINNER AT GRILLBY’S.” Papyrus asked, “SHE MADE SPAGHETTI WITH THE HUMAN AND FLOWEY, BUT THEY BURNED HER HOUSE DOWN, SO SHE’LL BE ‘CRASHING’ AT OURS AGAIN.”   
“Yeah bro, sure.” He replied, slightly annoyed that another moment to tell his brother had slipped away. Papyrus called out as he walked away, “I’LL MEET YOU THERE IN HALF AN HOUR, AS I’M GOING TO PICK UNDYNE UP FROM HERS.”

As Sans watched his brother walk away, the soul sent waves of happiness to Sans that said ‘uncle funny’.  
“yeah kiddo, your uncle is really funny.”


End file.
